The invention relates to a disc brake, in particular for a motor vehicle, having a brake application device, a brake caliper, in particular a sliding caliper which straddles a brake disc, preferably a lining wear adjusting device, and a brake carrier with guide faces which lie opposite one another in the circumferential direction of the brake disc. The invention also relates to a corresponding brake pad.
Disc brakes of this type are usually actuated pneumatically by compressed air and are equipped with automatically acting, mechanical lining wear adjusting devices. The lining wear adjusting devices reduce an air play (gap) which has become too large due, for example, to the wear of the brake pad or brake disc.
In the case of combined heavy trucks (such as tractor-trailer combinations), residual grinding torques of the wheel brakes, in particular of disc brakes, can increase fuel consumption by up to 1%. Moreover, increased brake pad wear occurs as a consequence of the constant grinding of the brake pads, as a result of which the maintenance costs of the vehicle are increased. A cause of said residual grinding torques is an incomplete release of the brake pads from the brake disc after a braking operation.
In order to avoid said residual grinding torque, it is necessary to produce a minimum air gap (minimum air play) between the friction faces of the brake pads and the brake disc friction face during release of the brake after a preceding braking operation by actively withdrawing the brake pads. Different methods are known for this purpose.
In the case of fixed caliper disc brakes which have a fixed position of the brake caliper and brake disc, it is sufficient to connect the brake pads to the actuating piston, which acts on the respective brake pad, in such a way that, during release of the brake, the actuating pistons also drive the brake pads in their withdrawal movement. In this way, the air play between the brake pads and brake disc is re-established. The avoidance of residual grinding torque to a great extent is possible by way of this measure in the case of fixed caliper disc brakes.
In the case of sliding caliper disc brakes, in contrast, sufficient release of the brake pads cannot be achieved solely by way of a withdrawal-capable attachment of the brake pads to the actuating pistons or to the caliper backs, since the brake caliper remains freely movable in its sliding guide. This can lead to one of the two brake pads, as a rule the caliper-side brake pad, still remaining in grinding contact with the brake disc.
In the case of sliding caliper disc brakes, it is therefore taken into consideration to impart a position which is, as it were, fixed to the brake caliper in the non-actuated state with the aid of clamping elements which are arranged on the sliding guides, as a result of which it is made possible to set the air play on both sides. This is illustrated by DE 10 2007 001 213 B4. This solution is relatively complicated and can be susceptible to disruption. In particular in the application in disc brakes which are actuated by compressed air for heavy commercial vehicles, this can be affected by influences which are variable within broad limits as a result of component tolerances and component deformations, which stands in the way of the application of said method (lining compressibility, wear state of the linings, caliper deformation, actuation force of the adjusting device, clamping force of the clamping ring, force of the restoring spring).
DE 22 30 949 C3 describes a brake pad guide for a partially lined disc brake, in which the influence of the sliding caliper and therefore of its component tolerances is largely ruled out. Here, the brake pad is supported directly in a frictionally locking manner via clamping elements against the guide faces of the stationary brake carrier. Upon actuation of the brake, the clamping elements are held on the guide faces as a result of the spreading force of a leaf spring, whereas the brake pad can perform a limited movement under the action of the actuating force of the brake, in order to come into sufficient frictional contact with the brake disc. After the brake actuation, the brake pad is pulled back into its starting position by way of the leaf spring which is fastened firstly on the brake pad and secondly on the clamping elements, and the air play is thus produced. If lining and/or brake disc wear occurs, the lining carrier plate reaches the stops on the travel limiting means of the clamping elements in the case of brake actuations, as a result of which the clamping elements are displaced in the direction of the brake disc under the action of the actuating force of the brake counter to their clamping force by an amount which corresponds to the wear which has occurred.
This method, which seems to be simple and practicable, has also not found any significant application. The clamping elements can be susceptible to contamination and corrosion. If vibrations occur, they can be subjected to pronounced loadings by the brake pad. In addition, the clamping elements can impair the action of the brake as a result of rusting up/blocking This solution is therefore not suitable for application in heavy commercial vehicles.
The object of the present invention consists in providing an improved disc brake.
It is a further object to provide an improved brake pad for a disc brake.
The disc brake according to the invention has, in each case, one restoring device for at least the reaction-side brake pad, the release function of which restoring device is not influenced by the brake caliper. The restoring devices have a simple construction and high robustness. A disruption in the action of the restoring devices does not cause the disc brake to be influenced. The disc brake can be actuated by compressed air and is particularly suitable for heavy commercial vehicles, residual grinding torques and unnecessary brake pad wear being avoided.
A disc brake according to the invention, in particular for a motor vehicle, comprises a brake application device, a brake caliper, in particular a sliding caliper, which straddles a brake disc, preferably a lining wear adjusting device, a brake carrier with guide faces which lie opposite one another in the circumferential direction of the brake disc, between which guide faces in each case at least one brake pad with a lining carrier is guided displaceably parallel to a rotational axis of the brake disc on both sides of the brake disc and can be actuated by a brake application force, and in each case one restoring device which supports at least the reaction-side brake pad with the lining carrier on the brake carrier. Each restoring device comprises at least two restoring elements which are attached on the lining carrier of at least the rear-side brake pad such that they can be guided displaceably parallel to the rotational axis of the brake disc.
As a result of the application of suitable restoring elements, further components which are susceptible to disruption, such as clamping elements, can be avoided and the number of components is reduced.
It is provided according to one advantageous design variant that the restoring elements are configured as sleeves which are mounted in receptacle holes of the lining carrier such that they can be displaced parallel to the rotational axis of the brake disc, from which sleeves in each case one restoring head, which can be restored elastically counter to a predefined force, protrudes toward the brake disc. The restoring head can be supported on a supporting face which protrudes from the guide faces in the circumferential direction of the brake disc. Releasing of the brake pad after the brake operation has taken place is made possible in a simple way via the restoring head which is supported in the sleeves.
The receptacle holes are preferably provided in depressions which are formed on the lining carrier on the outer edge regions in the circumferential direction of the brake disc, in order to provide sufficient installation space for the restoring head and the elastic elements and its support, even in the case of advanced wear of the friction linings of the brake pad.
In order to keep the friction lining area which acts on the friction face of the brake disc as great as possible, each of the friction linings of the brake pad is configured in each case with cutouts. These cutouts reach at least partially around the restoring elements.
The outer casing of the restoring elements is advantageously configured as a clamping sleeve. This ensures, firstly, a secure seat of the restoring elements in the lining carrier and, secondly, also the necessary displaceability of the restoring elements in the receptacle holes of the lining carrier.
It is also contemplated in an alternative design variant that the outer casing of the restoring element is provided with a knurled portion which is displaced further and further away from the brake disc through the receptacle hole of the lining carrier in the case of increasing lining wear. This variant likewise makes a secure seat and the necessary displaceability of the restoring element possible.
The restoring head preferably has a pressing face, and an axle body which protrudes into the outer casing perpendicularly with respect to the pressing face. The axle body is held in an oversprung manner in the outer casing according to one design variant.
In an alternative design variant, the axle body is supported on at least one spring, in particular a helical or disc spring, which is mounted in the outer casing.
In order to limit the displacement of the restoring head into the outer casing of the restoring element, the pressing face can preferably be supported on an end side of the outer casing, which end side faces the supporting face.
In order to ensure both the release of the brake pad from the brake disc and the adjustment of the restoring elements as a consequence of the friction lining wear, the restoring elements are held in a stationary manner in the lining carrier up to a force which acts parallel to the rotational axis of the brake disc and is smaller than the brake application force which is applied by the brake application device in the case of a braking operation. As a result, during the brake application in the case of a braking operation, each of the restoring elements can be pushed correspondingly in the receptacle hole of the lining carrier to a position, in which the friction lining bears against the brake disc and the restoring head bears against the supporting face of the brake carrier. After the braking operation or the brake application of the brake has ended, the prestressing force of the restoring head acts in the outer casing of the restoring element in such a way that the brake pad is pressed back from the brake disc and presses the brake pad back into its starting position with the re-establishment of an air play between the brake pad and brake disc.
In a further advantageous design variant, the restoring devices have restoring forces of different magnitude on different sides of the brake disc. This can result in a uniform division of the two-sided air plays.
Moreover, the restoring elements, which are configured as sleeves, can additionally also be configured with a different stiffness characteristic, for example, by way of the selection of the spring. This makes it possible that the restoring element with the larger stroke registers a more pronounced drop in force, as a result of which an action which equalizes the air plays occurs.
A corresponding brake pad of a disc brake is equipped with an above-described restoring device.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.